The present invention relates to true color image compression and reconstruction. More particularly, the present invention relates to lossy compression and reconstruction using an image specific color transformation.
JPEG (pronounced xe2x80x9cjay-pegxe2x80x9d) is a standardized image compression mechanism. JPEG stands for Joint Photographic Experts Group, the original name of the committee that wrote the standard. JPEG is designed for compressing either full-color or gray-scale images of natural, real-world scenes. It works well on photographs, naturalistic artwork, and similar material; not so well on lettering, simple cartoons, or line drawings. JPEG handles only still images. JPEG is xe2x80x9clossy,xe2x80x9d meaning that the decompressed image isn""t quite the same as the one you started with. JPEG achieves much greater compression than is possible with lossless methods. JPEG is designed to be lossy, and thus exploits the known limitations of the human eye. More specifically, the fact that small color changes are perceived less accurately than small changes in brightness. Thus, JPEG is intended for compressing images that will be looked at by humans. In contrast, the small errors introduced by JPEG may be a problem for images intended to be machine-analyzed.
A useful property of JPEG is that adjusting compression parameters can vary the degree of lossiness. This means that the image-maker can trade off file size against output image quality. You can make extremely small files if you don""t mind poor quality, such as indexing image archives. Conversely, if you aren""t happy with the output quality at the default compression setting, you can increase the quality until you are satisfied, and accept lesser compression.
The JPEG compression algorithm may be implemented in both software and hardware. For example, C-Cubed Microsystems introduced the first JPEG chip for compressing digital video images. Hardware provides the requisite speed for real-time compression. JPEG++, an algorithm described in U.S. Pat. No. 5,014,198, developed by Storm Technology, is an extension to JPEG.++ JPEG allows selected picture areas to be compressed at different ratios depending on the significance of the visual impact to the area in the image.
A problem with the traditional JPEG algorithm, and each of the aforementioned techniques, is that they all employ a fixed color space transformation. Generally, a fixed color space transformation is employed to transform an image from RGB into a luminance/chrominance color space (i.e., xe2x80x9cYUVxe2x80x9d), where luminance is the first component and chrominance the second and third components. To perform the transform a fixed predetermined matrix is employed that transforms the image from a RGB color space into a luminance/chrominance color space represented in an unsigned byte form (i.e., xe2x80x9cYCrCbxe2x80x9d). The rationale for using a luminance/chrominance color space is that some chrominance information can be lost in an image since the human eye is less likely to perceive the changes in the chrominance or color component of a reconstructed image. As a result, the chrominance components are subsampled or reduced, while the luminance component is left at full resolution.
Unfortunately, the use of a predetermined matrix to execute the transformation does not assure that the most information is presented in the first component because it does not consider the wide variety of possible scene content. More specifically, the transformation does not actively control or attempt to provide the most information about an individual image in the first component. Consequently, all images are treated equally despite the errors that may occur when reconstructing a compressed image, and thus affect image perception. Accordingly, images or applications that have a lower tolerance for loss are compressed at lower ratios since more information in the second and third components is required. This results in larger files, and thus less file storage space. In addition, larger files require significantly more time to transmit from a host to a remote site than smaller files. As a result, a method is needed that provides optimal image compression to improve file storage capacity and transmission time, while reducing image quality degradation.
Based on the above and foregoing, it can be appreciated that there presently exists a need in the art for a computer system and corresponding operating method which overcomes the above-described deficiencies. The present invention was motivated by a desire to overcome the drawbacks and shortcomings of the presently available technology, and thereby fulfill this need in the art.
It is therefore a feature and advantage of the present invention to provide an image compression and reconstruction technique that improves the image quality of a reconstructed image.
It is another feature and advantage of the present invention to reduce image quality degradation at high compression ratios.
It is another feature and advantage of the invention to optimize utilization of file space.
It is a further feature and advantage of the invention to compress a color image utilizing a transformation that is different for each image.
It is another feature and advantage of the invention to generate a transformation based on the color image""s color distribution.
It is a further feature and advantage of the invention to reduce transmission time in sending compressed images.
Further features and advantages of the invention will become apparent to those skilled in the art with reference to the accompanying figures and written description below.
The present invention is a system, method, and computer program product for compression and reconstruction of a color image using principal components transformation. The method is performed on a computer or other programmable data processing apparatus. The method is performed in combination with the standard JPEG image compression technique. According to the invention, the method receives color image information. The received color image information is converted into intrinsic color information. The intrinsic color information is based on the color image""s intrinsic and unique color distribution. This intrinsic color information characterizes the color image in a manner that increases the image quality of a reconstructed image, reduces the size of a compressed file as well as image transmission time.